LCD devices are commonly used as displays for compact electronic apparatuses. This is because they not only provide good quality images with little power consumption, but they are also very thin. The liquid crystal material in an LCD device does not emit any light itself. The liquid crystal material has to be lit by a light source so as to clearly and sharply display text and images. Thus, a backlight module is generally needed for an LCD device.
Referring to FIG. 9, a conventional LCD device 10 includes an upper polarizing film 101, a liquid crystal panel 100, a lower polarizing film 105, and a backlight module 120. The upper polarizing film 101 and the lower polarizing film 105 are attached on surfaces of two opposite sides of the liquid crystal panel 100, respectively. The backlight module 120 provides light beams to illuminate the liquid crystal panel 100. The liquid crystal panel 100 includes an upper substrate 102, a lower substrate 104, and a liquid crystal layer 103 between the upper and lower substrates 102, 104.
The backlight module 120 includes an upper brightness enhancement film (BEF) 121, a lower BEF 122, a diffusing film 124, a light guide plate (LGP) 126, a reflective film 128, and a light source 127. The LGP 126 has a light incident surface 1261, a top light emitting surface 1262 adjacent to the light incident surface 1261, and a bottom surface 1263 adjacent to the light incident surface 1261. The upper BEF 121, the lower BEF 122, and the diffusing film 124 are arranged in that order from top to bottom above the light emitting surface 1262. The reflective film 128 is arranged at the bottom surface 1263. The light source 127 is adjacent to the light incident surface 1261. The backlight module 120 is a side-edge type backlight unit, and the light source 127 may be a cold cathode fluorescent lamp (CCFL).
The upper BEF 121 includes a main body 1211, and a plurality of linear prism structures 1212 formed at a top of the main body 1211. The lower BEF 122 is similar to the upper BEF 121. However, linear prism structures (not labeled) of the lower BEF 122 are perpendicular to the prism structures 1212 of the upper BEF 121.
Referring to FIG. 10, the lower polarizing film 105 includes an adhesive layer 110, a protective film 112, a polarizing base 114, and a supporting plate 116, stacked in that order from top to bottom. The adhesive layer 110 is attached on the lower substrate 104 of the liquid crystal panel 100. The supporting plate 116 is used to support the polarizing base 114, and the protective film 112 is used to protect the polarizing base 114. The upper polarizing film 101 has a structure substantially the same as that of the lower polarizing film 105.
The backlight module 120 is a side-edge type backlight unit. Therefore the LGP 126 converts linear light beams emitted by the light source 127 into planar light beams. However, the conversion may be imperfect or incomplete, with the planar light beams being non-uniform. Furthermore, the upper BEF 121, the lower BEF 122, the diffusing film 124, the LGP 126, the reflective film 128, and the light source 127 are all separate components of the backlight module 120. This makes the process of assembly of the backlight module 120 rather complicated, and increases the rate of defects occurring in mass production of the backlight module 120.
What is needed, therefore, is a backlight module that can overcome the above-described deficiencies. What is also needed is an LCD device employing such a backlight module.